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Fraunhofer FDK AAC codec library. This is currently the highest-quality AAC encoder available with ffmpeg. Requires ffmpeg to be configured with `--enable-libfdk_aac` (and additionally `--enable-nonfree` if you're also using `--enable-gpl`). But beware, it defaults to a low-pass filter of around 14kHz. If you want to preserve higher frequencies, use `-cutoff 18000`. Adjust the number to the upper frequency limit you prefer.

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The Fraunhofer FDK AAC codec library. This is currently the highest-quality AAC encoder available with ffmpeg. Requires ffmpeg to be configured with `--enable-libfdk_aac` (and additionally `--enable-nonfree` if you're also using `--enable-gpl`). But beware, it defaults to a low-pass filter of around 14kHz ([[http://wiki.hydrogenaud.io/index.php?title=Fraunhofer_FDK_AAC#Bandwidth|details]]). If you want to preserve higher frequencies, use `-cutoff 18000`. Adjust the number to the upper frequency limit you prefer.

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Detailed information about the FDK AAC library (not FFmpeg specific) can be found at the [[http://wiki.hydrogenaud.io/index.php?title=Fraunhofer_FDK_AAC|Fraunhofer FDK AAC]] page in the HydrogenAudio Knowledgebase.

VBR encoding in libfdk-aac is '''experimental''' and only works with some parameter combinations. Target a ''quality'', rather than a specific ''bit rate''. 1 is lowest quality and 5 is highest quality. This mode is not compatible with [[#fdk_he|AAC-HE]]. Set the VBR level with the `-vbr` flag.

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According to [[http://www.hydrogenaudio.org/forums/index.php?showtopic=95989|this hydrogenaudio post]], the VBR modes (on average, over a number of files) give the following bit rates per channel (so for stereo, double the bit rate; for 5.1 surround sound, multiply it by six):

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VBR modes give the following bit rates per channel ([[http://wiki.hydrogenaud.io/index.php?title=Fraunhofer_FDK_AAC#Bitrate_Modes|details]]):